client.current and createScopedClient resolve transport via dispatchFor:
web -> absolute origin + /api base with an X-Honcho-Upstream header; Tauri ->
absolute instance URL + reqwest. Absolute base (not bare "/api") so openapi-fetch
can construct a Request under node/undici and in the browser alike. Fleet fan-out
is unchanged; fleet.test.tsx now asserts the proxy contract.